In control magnet assemblies of this kind, which are known in both flat-bed knitting machines and circular knitting machines (for example, see German Auslegeschrift No. 15 85 206, German Patent No. 20 10 973, German Offenlegungschrift No. 21 50 360 and German Offenlegungschrift No. 25 19 896), a variably large number of armature elements are retained on the selection magnet, in accordance with the triggering by the pattern apparatus in the through travel direction following the control pole zone. These armature elements form magnetic short-circuits with respect to the armature element that at a given time is actually in the control pole zone. As a result the retaining force with which that particular armature element is retained in the control pole zone is varied, and hence also the magnitude of the counter field that is to be built up relative to the permanent magnetic field, so as to reduce the retaining force to zero or to the vicinity of zero in the control pole zone for "throwing off" an armature element. In other words, the magnetizing current to be expanded to generate the counterforce and which is to flow through the control coils is dependent in its magnitude on how many armature elements remain attracted immediately previously. The fewer armature elements continue to adhere, the greater must the magnetizing current be that must flow through the control coil. This problem arises to an even greater extent in multi-system knitting machines or selection magnet systems, because the neighboring pole zones "throw off" in various ways. The same applies to flat-bed knitting machines, in contrast to circular knitting machines; in circular knitting machines, armature elements are always presented, while in the case of flat-bed machines this is not the case in the stroke reversal zones, where quite variable magnetic conditions therefore prevail.
In the known control magnet assemblies, optimal throwing off by the particular armature elements does not take place because the magnetic counterforce generated by the always-constant magnetizing flow through the control coil may possibly be too large or too small, which in either case can cause an armature element that should be thrown off to remain stuck. Although it is known from German Offenlegungschrift No. 21 50 360 to provide the selection magnet with an adjustable magnetic shortcircuit, nevertheless all this means is that manufacturing tolerances and material deviations which affect the magnetic circuit can be compensated for. The above-described problem or disadvantage still exists, however.